Abstract

[1] Most food production depends, directly or indirectly, on freshwater resources. In the absence of importation of food commodities, population growth is constrained by the availability of local resources—including water—as well as by cultural and health-related factors. The global trade of massive amounts of food makes societies less reliant on locally available water resources, thereby allowing some populations to exceed the limits posed by their local water budget. Thus, international trade implies a virtual transfer of water resources from areas of food production to importing regions. While it is recognized that in the short term this globalization of (virtual) water resources may prevent malnourishment, famine, and conflicts, its long-term effects on the coupled human-natural system remain poorly investigated. Here we develop a minimalist modeling framework to investigate the effect of the uncontrolled trade of food products on the resilience of human societies with respect to drought and famine. Our results suggest that in the long run the globalization of water resources reduces the societal resilience with respect to water limitations in that it leaves fewer options available to cope with exceptional droughts and crop failure.

Water is vital for human life. It is used for not only drinking but also producing electricity, washing, cooking, and growing food. Lately there has been a disproportionate population growth in arid regions, and the demand for water in those regions exceeds the limited supply. However, through the importation of food from other regions, water is virtually transported to arid regions. This exchange allows some societies to thrive in a water-deficient state and prevents water wars. However, D'Odorico et al. (2010) suggest that this increased globalization of water supplies can actually decrease the chance for human societies to rebound from drought-induced crop failure. The researchers used a simplistic model of population dynamics to study exchanges of virtual water. They considered a situation in which water is shared only locally, a situation in which water is shared globally only when a drought in one region necessitates sharing, and a situation in which water is shared globally at all times. They found that when water is shared globally at all times, populations can grow worldwide, including in arid regions. This works well as a short-term solution, but in the long term, global water supplies are stressed, leaving little extra water capacity to deal with a drought-induced famine in one region and leading to increased mortality during droughts. However, the simulation showed that when water was shared globally only during times of drought, unused water capacity was available and could be shared with the region needing water, thus making society more resilient.